Smoke detector

ABSTRACT

A smoke detector of the type utilizing photo-electric detection of light reflected from smoke particles, in which a lightgenerating device is energized intermittently and a photoresponsive device and an associated amplifier produce energy pulses when smoke is present. The energy pulses are utilized to actuate an alarm. To prevent power supply voltage changes from affecting the operation of the amplifier, a capacitor is provided across the power leads to the amplifier, and means is provided between the capacitor and the power supply for electrically isolating the amplifier and capacitor from the transient voltages from the power supply, which are caused by the turning on of the light generating device, or from other causes. In one embodiment of the invention said means comprises a choke coil in the line to the capacitor and a second choke coil in the line to the light generating device. In another embodiment of the invention the isolating means may be Zener diodes in place of choke coils. In a third embodiment of the invention the means comprises a switch in the power line between the capacitor and the power supply, with means being provided to open the switch when the light generating device is energized. In each embodiment, the amplifier is isolated from transient voltage changes during the time the light generating device is energized, so that the pulse of energy required to power the amplifier is provided by the capacitor.

United States Patent Malinowski I SMOKE DETECTOR [75] Inventor: William J. Malinowski, Pembroke,

Primary Examiner-James W. Lawrence Assistant Examiner-E. R. La Roche Attorney, Agent, or Firm-Robert E. Ross [57] ABSTRACT A smoke detector of the type utilizing photo-electric detection of light reflected from smoke particles, in which a light-generating device is energized intermit- Nov. 4, 1975 tently and a photo-responsive device and an associated amplifier produce energy pulses when smoke is present. The energy pulses are utilized to actuate an alarm.

In one embodiment of the invention said means comprises a choke coil in the line to the capacitor and a second choke coil in the line to the light generating device. In another embodiment of the invention the isolating means may be Zener diodes in place of choke coils. In a third embodiment of the invention the means comprises a switch in the power line between the capacitor and-the power supply, with means being provided to open the switch when the light generating device is energized. In each embodiment, the amplifier is isolated from transient voltage changes during the time the light generating device is energized, so that the pulse of energy required to power the amplifier is provided by the capacitor.

9' Claims, 3 Drawing Figures zw I ii U.S. Patent Nov. 4, 1975 u m R wk u 2% \k F I I l l I l l I I ll SMOKE DETECTOR BACKGROUND OF THE INVENTION Various types of smoke detectors are known which comprise a pulsing light source, a photo-responsive device to receive light pulses reflected from smoke particles and an amplifier for amplifying voltage pulses from the photo-responsive device into a magnitude such that they can be utilized to actuate an alarm.

It is often desired for certain installations that such devices be powered from a battery, however one difficulty with a battery power source results from the fact that when the light source is turned on, the internal impedence of the battery causes the voltage at the terminals to drop. If the amplifier is powered from the same battery, the voltage to the amplifier also drops, which creates a transient signal in the amplifier which may produce an output signal many times greater than the output signal produced by the photo-responsive device when smoke is present, and it is difficult or impossible to separate the two signals.

The same problem may occur when a plurality of smoke detectors are connected to a loop from a common power source at a central control panel. Since detectors of this type draw very little current, one of their great advantages is the fact that small wire can be used for connecting them to the central control panel. However since the instantaneous current, on the energization of the light emitting device, may be as high as 7 amperes, a substantial voltage drop at the terminals of the smoke detector can occur, which would produce a false signal in the amplifier.

Various means have been used to prevent such transient changes in the power supply voltage. For example, it is possible to power the amplifier and the light emitting device from separate batteries. It has also been proposed that the amplifier should be normally off, and turned on only after the light emitting device is turned on. In a loop system powered from a central control panel, it is possible to run separate power supply wires for the light emitting devices and the amplifiers. All of these expedients involve additional expense that is not acceptable in the majority of smoke detector applications.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic drawing of a smoke detector circuit embodying the features of the invention, in which the amplifier is isolated from the power supply, during the time that the light-emitting device is on, by means of a switch which opens when the light emitting device is turned, so that during the period when the amplifier is likely to receive a signal from the photoresponsive device, the amplifier, and associated equipment, is being powered solely by the storage capacitor.

FIG. 2 is a schematic drawing of the detector of FIG. 1 in which choke coils are utilized to isolate the amplifier from voltage transients created when the light emitting device is turned on.

FIG. 3 is a schematic drawing of the detector of FIG. 1 in which Zener diodes are provided in the separate power leads to the amplifier and the light emitting device.

Referring to the drawing, there is illustrated an electronic circuit for use in a smoke detector of the type operating on the reflected light principle. The circuit includes a light emitting diode LED and a photo-voltaic 2 cell C positioned out of the direct line of the beam of light from the LED. In a preferred embodiment of the invention the cell C is positioned to view a portion of the beam, in front of the LED at an angle of about to about l35 to the axis of the beam, to take advantage of the well known forward scatter effect.

The cell C is coupled through capacitor F to an amplifier A, the output of which is fed to a level detector L such as a differential comparator. The level detector output is fed to the set terminal of a flip-flop circuit FF, the output of which is fed to an integrator T, which energizes an alarm actuating device R. k

In a preferred embodiment of the device, the differential comparator is normally off with the signal lead thereof being clamped to ground by an electronic switch 81.

To energize the LED on an intermittent basis, a pulse generator P is provided which, in addition to providing an energizing pulse to the LED, also simultaneously applies a pulse to energize the level detector and applies a pulse to the re-set terminal of the flip-flop through discriminator D, which converts the pulse to a spike of voltage applied to the reset terminal at the beginning of the pulse cycle.

The above described portion of the circuit is disclosed and described in more detail in my copending application Ser. No. 419,206 filed Nov. 26, 1973, and is used here as an example of a smoke detector into which the present invention may be incorporated.

In the modification of the present invention illustrated in FIG. I, one lead W2 is provided from the power source V1 to the pulse generator, and a second lead W1 is provided from the power source to the amplifier, the level detector, and the flip-flop.

The line W1 contains a series connected electronic switch S2 between the power source and the components energized by said line, and capacitors F1 and F2 are connected between ground and the lines W1 and W2, respectively, at a point between the pulse generator and the power source.

In the embodiment of FIG. 1, the pulse generator, in addition to the functions previously described, also applies a pulse to the switch S2 to open said switch and thereby disconnect the amplifier and associated equipment on lead W1 from the power source during the time that the LED is energized, so that during this period, the amplifier and associated equipment operates solely from the charge stored in the capacitor F1.

The operation of the device may be summarized as follows:

As in the above identified co-pending application, the duration of the pulse which energizes the LED is very short, for example, 20 micro-seconds compared to the repetition rate, which is 1 or 2 seconds.

During the time that the pulse generator is off, capacitors F1 and F2 are charged from the power source V 1. When the pulse generator applies an energizing pulse to the LED, it simultaneously applies a pulse to the switch S2 to open said switch. The amplifier and other equipment on line W1 are therefore, at the instant that the LED is turned on, disconnected from the power supply, and the energy necessary to operate the amplifier comes only from the capacitor F1.

As described in my co-pending application, if smoke is present, pulses of light are reflected therefrom and fall on the photo-cell C, causing a series of voltage pulses at the input of the amplifier. If the amplified pulses are of sufficient magnitude to satisfy the require- 3 ments of the level detector, a series of pulses are applied to the *set" terminal of the flip-flop, which applies a series of pulses (since the flip-flop is re-set at the beginning of'each pulse) to the integrator, to actuate the alarm.

At the end of each pulse to the LED, the switch S2 closes so that the capacitor can recover the small amount of charge used in powering the amplifier and associated equipment.

In the particular illustrated embodiment,'the current used to power the LED may be of the order of 7 to 10 amperes. Although this current is drawn for only micro-seconds, it would nevertheless cause a sudden and substantial drop in the voltage at the amplifier (unless the impedence of the voltage source is so low that it would be impractical for a commercial installation). Without the presence of the switch S2 and capacitor Fl, a substantial drop in supply voltage to the amplifier would occur. Such drop in voltage would cause a sudden change in bias voltage in the amplifier, which would be interpreted by the amplifier as a signal, which could either cause or negate an alarm (depending on the phase relationship of the amplifier being used),

since the change in supply voltage of such a magnitude could cause an output signal from the amplifier which is many times the output signal that would be created by a signal resulting from light reflected from smoke particles.

If the system is being operated from a loop from a power supply at a central control panel, the isolation of the amplifier from the power supply by the opening of switch S2 during the time that the LED is emitting light also prevents transient voltages occurring on the loop from generating spurious responses in the amplifier.

Referring now to FIG. 2, there is illustrated a modified form of smoke detector, with the portion of the circuit shown therein enclosed in the dashed line being substituted for the portion of the circuit enclosed in the dashed line'of FIG. '1.-The circuit of FIG. 2 includes a choke coil CKl in place of switch S2, and a choke coil CK2 in series with the line to the pulse generator. The choke coilsCKl and CK2 have electrical characteristics such that when the pulse generator turns on the LED,.-the choke coils isolate the amplifier from the high frequency negative pulse caused by the sudden drop in power supply voltage. Since the power to the amplifier is'itself a high frequency pulse which could not pass through the choke coil CKl, the power for the operation of the amplifier is supplied substantially entirely by capacitor Fl.

Referring now to FIG. 3, there is illustrated a second modified form of smoke detector, with the portion of the circuit shown therein enclosed in the dashed line being substituted for the portion of the circuit enclosed in the dashed line of FIG. 1.

The circuit of FIG. 3 includes Zener diodes Z1 and Z2 connected between lines W1 and W2 respectively and ground, with resistors R1 and R2 being in series in lines W1 and W2 between the connection to the Zener diodes and the power source V2. In the circuit of FIG. 3, the power source V2 is higher than necessary to operate theamplifier and the pulse generator, and the voltage is regulated to the correct amount by the Zener diodes. 7

When the pulse generator turns on the LED, power is drawn from the capacitor F2, and voltage drop at the capacitor input is prevented by the regulating effect of the Zener diode Z2. Simularly, voltage to the amplifier 4 is regulated by the Zener diode Z1 so that no residual voltage change at the power source from the turning on of the LED or from other transients on the power line can affect the operation of the amplifier.

It will be understood that various combinations of the illustrated modifications can be used, depending on the particular installation. For example, when operated from battery power in which the same battery also powers the alarm device, the system of FIG. 1 may include a choke coil in line W2 to the pulse generator to prevent transients on the line resulting from the energizing of the alarm unit from affecting the operation of the pulse generator.

The switch S2 may, if desired, be incorporated into the modifications of FIGS. 2 and 3.

In any of the modifications of the invention or combinations thereof, it is essential that during the period that the amplifier is operative to amplify a pulse from the photo-generative device and pass it to the signalling device, the voltage on capacitors F1 and F2 be equal, except for the minute difference in voltage resulting from the fact that during the operative period, the light generating device may draw slightly more power from capacitor F2 than the amplifier and associated equipment draws from capacitor F1. However the capacitors are sufficiently large in relation to the power needed for the operation of the components that the voltage.

drop thereof is very small in relation to the supply voltage, and hence the voltage difference between the capacitors at the end of a pulse is inappreciable.

Although in the illustrated embodiment, the amplifier is energized continuously and the level detector is normally de-energized and energized only when the light emitting diode is emitting light, it will be understood that if desired the amplifier may be normally off, and energized only during some part of the period that the I light emitting diode is energized. Hence in the claims, when the term amplifier is used, it is intended to include the components of FIG. 1 labelled A, L, and FF, unless the context clearly indicates otherwise.

Since certain other changes apparent to one skilled in the art may be made in the illustrated embodiments without departing from the scope of the invention, it is intended that all matter contained herein be interpreted in an illustrative and not in a limiting sense.

I claim:

1. In a smoke detector of the type utilizing photoelectric detection of light reflected from smoke particles (in which) having a light source which is energized intermittently, first means including a photo-responsive device (is provided) and an amplifier to produce energy pulses in response to light pulses refected from smoke particles, and second means utilizing said energy pulses to control a signalling device, the improvement comprising a voltage supply for said first means, a capacitor connected across the voltage supply, and third means between the capacitor and the voltage supply for isolating the (amplifier) first means and the capacitor from voltage pulses occurring at the power supply at least during the time that the light source is emitting light.

2. A smoke detector as set out in claim 1 in which said third means allows current flow when the light source is not producing light, but effectively prevents the passing of voltage pulses in the frequency range to which the amplifier is responsive.

3. A smoke detector as set out in claim 1 in which means is provided for energizing said amplifier only while the light source is emitting light, and said third means allows current flow to charge the capacitor while the amplifier is de-energized but does not allow a voltage pulse to pass therethrough during the period that the amplifier is energized, whereby the amplifier draws power substantially only from the capacitor when it is energized.

4. A smoke detector as set out in claim 1 in which said third means is a switch, and means is provided to open said switch when the light sourceis energized and to close said switch when the light source is de-energized.

5. In a smoke detector of the type utilizing photoelectric detection of light reflected from smoke particles, in which a pulse generator pulses a light generating device, a photo-voltaic cell is positioned to produce voltage pulses from the pulsed light reflected from smoke particles, means is provided for amplifying said voltage pulses, and means is provided for utilizing said amplified pulses to control a signalling device, the improvement comprising said pulse generator and said amplifier being supplied by separate leads from a common power source, means rendering said amplifier operative substantially only during the time the pulse generator is on, a storage capacitor connected across the leads to the amplifier and an impedence device disposed between the storage capacitor and the power source, whereby when the amplifier is turned on, it draws power principally from the storage capacitor, and the impedence means isolates the amplifier from voltage transients at the power source due to the turning on of the pulse generator and the light generating device.

6. A smoke detector as set out in claim 5 in which said impedence means comprises an inductance having electrical characteristics such that it prevents passage of voltage pulses in the frequency range to which the amplifier is responsive.

7. A smoke detector having a light source, means en ergizing the light source intermittently, photo-responsive means positioned to receive light reflected from smoke particles illuminated by the light source, and amplifier means for amplifying voltage pulses resulting therefrom, a power source, means providing power therefrom to the light source and to the amplifier by first and second power leads, first and second capacitors associated with said first and second power leads respectively, and means between each capacitor and so as to be charged by said power supply the power supply for isolating said capacitors from transient voltages occuring at the power supply during the period that the light source is emitting light so that during said period the voltages on said first and second capacitors remain substantially equal.

8. A smoke detector as set out in claim 7 in which said means for isolating from the power supply the capacitor associated with the power lead to the amplifier includes a switch in said lead and means for opening and closing said switch with energization and de-energization of the light source.

9. A smoke detector comprising a light source, a photo-responsive device positioned to view light reflected from smoke particles illuminated by the light source, a pulse generator for providing energizing pulses to the light source, amplifier means for amplifying pulses created by the photoresponsive device, said pulse generator providing a pulse to render said amplifier operative only when said light source is energized, said pulse generator and said light source being energized by a first lead from a power source and said amplifier being energized by a second lead from said power source, a first capacitor connected in parallel with said amplifier and a second capacitor connected in parallel with the pulse generator, and means maintaining the voltage on said capacitors substantially equal while the light source is energized and the amplifier is operable. 

1. In a smoke detector of the type utilizing photo-electric detection of light reflected from smoke particles (in which) having a light source which is energized intermittently, first means including a photo-responsive device (is provided) and an amplifier to produce energy pulses in response to light pulses refected from smoke particles, and second means utilizing said energy pulses to control a signalling device, the improvement comprising a voltage supply for said first means, a capacitor connected across the voltage supply, and third means between the capacitor and the voltage supply for isolating the (amplifier) first means and the capacitor from voltage pulses occurring at the power supply at least during the time that the light source is emitting light.
 2. A smoke detector as set out in claim 1 in which said third means allows current flow when the light source is not producing light, but effectively prevents the passing of voltage pulses in the frequency range to which the amplifier is responsive.
 3. A smoke detector as set out in claim 1 in which means is provided for energizing said amplifier only while the light source is emitting light, and said third means allows current flow to charge the capacitor While the amplifier is de-energized but does not allow a voltage pulse to pass therethrough during the period that the amplifier is energized, whereby the amplifier draws power substantially only from the capacitor when it is energized.
 4. A smoke detector as set out in claim 1 in which said third means is a switch, and means is provided to open said switch when the light source is energized and to close said switch when the light source is de-energized.
 5. In a smoke detector of the type utilizing photo-electric detection of light reflected from smoke particles, in which a pulse generator pulses a light generating device, a photo-voltaic cell is positioned to produce voltage pulses from the pulsed light reflected from smoke particles, means is provided for amplifying said voltage pulses, and means is provided for utilizing said amplified pulses to control a signalling device, the improvement comprising said pulse generator and said amplifier being supplied by separate leads from a common power source, means rendering said amplifier operative substantially only during the time the pulse generator is on, a storage capacitor connected across the leads to the amplifier and an impedence device disposed between the storage capacitor and the power source, whereby when the amplifier is turned on, it draws power principally from the storage capacitor, and the impedence means isolates the amplifier from voltage transients at the power source due to the turning on of the pulse generator and the light generating device.
 6. A smoke detector as set out in claim 5 in which said impedence means comprises an inductance having electrical characteristics such that it prevents passage of voltage pulses in the frequency range to which the amplifier is responsive.
 7. A smoke detector having a light source, means energizing the light source intermittently, photo-responsive means positioned to receive light reflected from smoke particles illuminated by the light source, and amplifier means for amplifying voltage pulses resulting therefrom, a power source, means providing power therefrom to the light source and to the amplifier by first and second power leads, first and second capacitors associated with said first and second power leads respectively, and means between each capacitor and so as to be charged by said power supply the power supply for isolating said capacitors from transient voltages occuring at the power supply during the period that the light source is emitting light so that during said period the voltages on said first and second capacitors remain substantially equal.
 8. A smoke detector as set out in claim 7 in which said means for isolating from the power supply the capacitor associated with the power lead to the amplifier includes a switch in said lead and means for opening and closing said switch with energization and de-energization of the light source.
 9. A smoke detector comprising a light source, a photo-responsive device positioned to view light reflected from smoke particles illuminated by the light source, a pulse generator for providing energizing pulses to the light source, amplifier means for amplifying pulses created by the photoresponsive device, said pulse generator providing a pulse to render said amplifier operative only when said light source is energized, said pulse generator and said light source being energized by a first lead from a power source and said amplifier being energized by a second lead from said power source, a first capacitor connected in parallel with said amplifier and a second capacitor connected in parallel with the pulse generator, and means maintaining the voltage on said capacitors substantially equal while the light source is energized and the amplifier is operable. 